Of course at first I was a bit worried about support for my plugins , including Rikaichan, which I use all the time.

But here is how you can get all your old plugins working with FF4b1 even if they aren't officially supported yet!

Just click on the Firefox menu in the very top left of your browser, choose Customize, and then choose Add-ons (or simply go to about:addons in your address bar), and then click on Get Add-ons in the upper left.

This will take you to a page that says "Something good is coming!" with a little robot and a box beneath that that says "Help add-on developers get ready for Firefox 4 by installing the Add-on Compatibility Reporter"

Install that, restart Firefox, and then you will be taken to a page explaining how it works and asking you to restart one more time to enable the currently disabled (and marked as incompatible) add-ons.

Once you've restarted all your plugins should work again. If they do work the way you'd expect, you can go back to the about:addons page and click on the Compatibility button and choose "This add-on still works" to let the Firefox people know that the add-on still works fine. If it doesn't, you can also report it there so that they can let the developer know they still need to do some work.

Let me know if you have any trouble with this! I'll be glad to help. Firefox 4.0 Beta 1 is a great advancement to a great browser and worrying about whether or not your favorite add-ons will work shouldn't be a reason to avoid upgrading to the cutting edge.